There have been proposed heretofore various methods for the formation of electrophotographic color images wherein the cycle of charging, exposure and developing is repeated a plurality of times to form a plurality of toner images of different colors on an electrophotographic photoconductor (hereinafter called a photoconductor), the toner images then being transferred onto paper to reproduce a color copy image thereon.
As an example of apparatuses using such electrophotographic color image forming methods, the apparatus has been proposed by the inventors of the present invention in Japanese Patent Application No. 62-4367, is described below with reference to FIG. 2.
The reference numerals 1, 2, 3 and 4 indicate mono-component, non-magnetic developer units of non-contact type which project toner in a direct current electric field. The toner is charged triboelectrically with conductive fur brushes 5, 6, 7 and 8 which are disposed in a contacting array with respective developing rollers, thereby causing a thin layer of toner to form on the aluminum developing rollers 9, 10, 11 and 12 by means of respective blades 13, 14, 15 and 16. The developer unit 1 contains insulative toner of yellow (Y), the developer unit 2, magenta (M), the developer unit 3, cyan (C), and the developer unit 4 black (Bk). The developer units are disposed facing the circumference of a photoconductor 17, with a given gap (developing gap) provided between each of the developing rollers 9, 10, 11 and 12 and the photoconductor 17. Each developer unit is provided with a moving mechanism for causing it to move closer to the photoconductor 17 when developing is performed and to retract when developing is not performed. The following shows the specification and developing conditions of each developer unit, and the properties of the toner used.